Plasma Physics Reports最新文献

The frequency dependence of the energy and ion current at the output of an RF plasma source with SPT geometry has been investigated. It has been shown that the ion energy is maximum when operating at a frequency of 6.8 MHz. An increase in the operating frequency is accompanied by a decrease in ion energy. The ion current depends nonmonotonically on frequency. At frequencies less than 27.12 MHz, an increase in the ion energy is accompanied by a decrease in the current, and a decrease in the energy by an increase in the current. Increasing the frequency to 27.12 MHz does not lead to an increase in the ion current.

The paper presents the results of numerical simulation of the initial stage of expansion of plasma formations resulting from the injection of high-speed aluminum plasma jets into the Earth’s ionosphere at different altitudes corresponding to two “North Star” experiments. The influence of an artificial atmosphere represented by an air cloud on the plasma formation parameters in the North Star-I experiment is studied. Gas-dynamic parameters of plasma formations and their optical characteristics are determined. We present a comparison of the calculation results with the results of measurements of the luminosity curves in two wavelength ranges of photometers, which shows good agreement between the calculated and experimental data.

A method for prompt estimation of a number of key parameters that determine the features of the evolution and dynamics of current sheets produced in laboratory experiments has been proposed and realized experimentally. The method is based on the analysis of time dependences of the integral plasma current during its first half-period. The transverse dimensions of the current sheets and the strength of the initial electric field that initiates the sheet formation can be estimated on the base of defining the inductances of both the entire oscillatory contour and the region where the plasma current flows. Data on the plasma conductivity can be obtained by measuring the active resistance of the plasma gap and the dimensions of the current sheet. It is shown that the conductivity increased under conditions that corresponded to an increase in plasma density, indicating a turbulent nature of the conductivity.

Electric charging of dust grains lying on the surface of the Moon is caused by the action of the solar wind plasma and the solar UV radiation. Near the terminator and in the shadow the charges on dust grains are negative and not too high for electrostatic lofting of such grains. That is why very strong electric fields are required to explain dust motion above the surface. Due to this various factors are taken into account to obtain stronger electric forces acting on dust grains. In the present paper it is investigated how the dielectric permittivity of the regolith and subsurface layers influence charging of dust grains on the Moon. We show theoretically that the dielectric permittivity in some regions can provide stronger (one order of magnitude and even more) electric charges of dust grains on the surface than it was estimated before.

In 2023, the Thomson scattering diagnostics with tangential probing geometry was installed and put into operation at the T-15MD tokamak. The new system is based on a 100-Hz Nd:YAG laser with a pulse energy of up to 3 J at the first harmonic, λ = 1064 nm. The system allows measurements to be carried out throughout the plasma discharge with its duration of up to 10 s with a time interval of 10 ms. Laser radiation is introduced into the tokamak vessel in the equatorial plane, passing through the entire plasma volume from the inner to the outer periphery of the plasma. The scattered radiation acquisition system is located inside the equatorial port of the facility. The range of scattering angles is from 11° to 56°. The recording system is based on 10 polychromators on interference filters. Using this diagnostics, the electron temperature and density have been measured in the experimental campaign at the end of 2023. The system operation was demonstrated throughout the entire tokamak discharge in a wide temperature range and with a discharge duration of up to 2 s.

The radial distribution of the B_z field at a distance of 35 cm from the generation region of the axial jet emission (the anode surface of the setup) has been studied using the PF-3 plasma-focus facility. The measurements have been performed using multichannel magnetic probes located in the flight chamber of the facility. This has made it possible to measure the magnetic field distribution at 18 points on both sides of the flight chamber axis. The magnetic probes have been calibrated both in absolute value and in the magnetic field direction. An external multi-turn solenoid has been used to create the initial longitudinal (poloidal) magnetic field. The solenoid power supply circuit has allowed obtaining different B_z field directions: along or against the facility axis. It is shown that the poloidal field distribution reaches its maximum in the bunch center and decreases at the periphery, regardless of the presence of an external magnetic field. The B_z field has a radial distribution B_z(r), close in shape to the magnetic field distribution of the solenoid. The work is performed within the program for the simulation of jets of young stellar objects.

The system of MHD equations for the equilibrium states of plasma in a given potential field is reduced to a single differential equation.

Nonlinear resonant interaction between the electromagnetic ion-cyclotron (EMIC) wave and magnetospheric electrons at the Cerenkov resonance, also referred to as the Landau or the zero-order cyclotron resonance, is investigated. Based on the data obtained on September 10, 2017, by one of the Van Allen Probe (RBSP) spacecrafts, the trajectory of a monochromatic wave packet in an inhomogeneous multicomponent plasma is found. The amplitude of the wave along the propagation trajectory is calculated taking into account not only the linear resonant interaction with protons and electrons but also variation of geometric factors such as the group velocity and the ray tube cross section. Numerical integration of the nonlinear system of equations describing the motion of electrons in the field of modeled packet of the EMIC waves revealed an important role played by nonlinear effects in the dynamics of resonant particles.

Selecting the most effective and biologically safe operation regimes of a cold atmospheric plasma jet (CAPJ) is a defining factor in developing the cancer treatments based on the CAPJ. Experimentally and numerically, by changing the pulse duration of the positive pulsed voltage, we determined the optimum CAPJ regimes with regular propagation of streamers and a maximum discharge current at a temperature T < 42°C. In these regimes, the CAPJ appreciably suppresses the viability of the cancerous cells. It was shown that adding gold nanoparticles increases the cytotoxic effect of the plasma jet and decreases the viability of the NCI‑H23 epithelioid lung adenocarcinoma, the A549 lung adenocarcinoma, the BrCCh4e-134 mammary adenocarcinoma, and the cells of the uMel1 uveal melanoma. The polyethylenglycol-modified gold nanoparticles with fluorescent labels were used to visualize the absorption of the nanoparticles by the cells. It was shown that the CAPJ stimulated the penetration of the nanoparticles into the cells when they were applied to the medium immediately before the CAPJ treatment or immediately after, which indicates a short-time increase in the permeability of the cell membrane.

The results of the numerical simulation of a pulse-periodic nanosecond discharge are presented. An axisymmetric high-frequency (5 MHz) electric discharge in a pin-to-pin configuration is considered. Numerical models are used that take into account the chemical kinetics of high-temperature air and plasma chemistry, in which the reaction rates are determined by the magnitude of the reduced electric field. Preliminary results of plasma activation of atmospheric pressure air by a pulse-periodic nanosecond discharge are presented in order to intensify the production of chemically active particles (by the example of atomic oxygen).